The present invention generally relates to corrosion monitoring technology, and more particularly to a method and system for online corrosion monitoring of turbomachinery components, such as blades within a compressor section of a gas turbine.
Components of turbomachines, including those of gas turbines employed for power generation and propulsion, are subject to damage from corrosion, oxidation, and contamination by agents present in the airflow of the turbomachine during its operation. For example, in corrosive environments such as near and offshore regions and industrial facilities, gas turbine compressors may suffer relatively high pitting corrosion rates due to water condensation on the blades of their first several stages, combined with fouling deposits and chloride and/or sulfate air pollutants. To maintain compressor health, industrial gas turbine operators perform various maintenance actions, typically including online and/or offline water washes, offline inspections, and filter maintenance. Understandably, disadvantages exist if these tasks are performed too frequently or infrequently. For example, excessive online washing can promote erosion, while insufficient online washing results in increased corrosion rates due to buildup of corrosive agents on the compressor blades. Inevitably, offline inspections must be performed, requiring turbine shutdown and dismantlement that incur downtime. Though offline inspections are very costly events, failing to timely perform these inspections can result in damage to the turbine, such as from liberation of a compressor blade due to pitting corrosion. Consequently, gas turbine operators rely on carefully scheduled offline inspections to monitor compressor health and perform repairs to avert destructive events.
Complete results from offline inspections are often unavailable for several months, and can be difficult to directly correlate to actual compressor corrosion/pitting rates present in the compressor. Therefore, it would be desirable to minimize offline inspections by providing turbine operators with realtime information on the compressor status, such that appropriate maintenance activities can be taken when and as necessary to prolong compressor life in corrosive environments. However, many factors complicate efforts to determine through online monitoring the presence and extent of corrosion on compressor components of industrial gas turbines. Complicating factors include the operating parameters of the machine, washing intervals and methods, filter type and maintenance, and various other variables. For many industrial gas turbines, filter maintenance and failure, seal leakage, and emissions from neighboring facilities can have a significant and unpredictable impact on corrosion rates. Other conditions that can affect corrosion rates include the operational parameters of the compressor, such as turndown, startup/shutdown amount, etc.
From the above, it can be appreciated that, to avoid reliance on confusing operational and environmental indicators for the purpose of making timely operational and inspection decisions, gas turbine operators would require realtime (online) measurements of corrosion rates of the gas turbine components, and a comprehensive set of maintenance instructions based on those measurements.